1. Field of the Invention
The present invention relates to a surface treatment method of a group III nitride semiconductor, a group III nitride semiconductor, a manufacturing method of the same and a group III nitride semiconductor structure, and more particularly, to a surface treatment method of a group III nitride semiconductor in which opposing two surfaces have identical polarity, a group III nitride semiconductor, a manufacturing method of the same and a group III nitride semiconductor structure.
2. Description of the Related Art
In general, a light emitting device formed of a group III nitride semiconductor is utilized to obtain light in a blue or green wavelength. The light emitting device is made of a semiconductor material having a composition expressed by AlxInyGa(1−x−y)N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1.
A group III nitride semiconductor can be grown on a heterogeneous substrate such as a sapphire (α-Al2O3) substrate and a SiC substrate. Particularly, the sapphire substrate has a hexagonal structure identical to a gallium nitride. Moreover, the sapphire substrate is cheaper than the SiC substrate and stable at a high temperature, thus mainly employed as a growth substrate for the group III nitride semiconductor.
Meanwhile, the group III nitride semiconductor grown on the sapphire substrate has a Wurtzite and non-centrosymmetric crystal structure. Therefore, the group III nitride semiconductor, for example, gallium (Ga) nitride semiconductor has a gallium polarity on one surface (hereinafter gallium polarity surface and a nitrogen (N) polarity on another surface (hereinafter nitrogen polarity surface). As described above, the two surfaces of the gallium nitride semiconductor experience physical differences in etching rate and surface recombination configuration, or defects and surface dislocation due to differences in surface polarity. These physical differences lead to differences in surface characteristics between the gallium polarity surface and the nitrogen polarity surface.
Specifically, the gallium polarity surface of the gallium nitride semiconductor exhibits a superior surface flatness than the nitrogen polarity surface. Also, the gallium polarity surface possesses better crystallinity than the nitrogen polarity surface due to low binding of materials acting as an impurity. Accordingly, when the gallium semiconductor is re-grown, a re-growth layer grown on the gallium polarity surface has a flat surface. Meanwhile, the re-growth layer grown on the nitrogen polarity surface suffers defects on a surface thereof such as hillock, column and pyramidal grain.
In the meantime, polarity differences between both surfaces of the gallium nitride semiconductor cause spontaneous polarization, thereby leading to differences in surface band bending between the gallium polarity surface and the nitrogen polarity surface.
Also, the gallium polarity surface of the gallium nitride semiconductor exhibits a low constant voltage due to low ohmic contact resistance, and possesses superior electrical characteristics than the nitrogen polarity surface. Moreover, the both surfaces of the gallium nitride semiconductor react differently to an etching solution, for example, ‘KOH’ owing to polarity differences. Specifically, the gallium polarity surface hardly reacts with the etching solution and the nitrogen polarity surface reacts actively with the etching surface and thus is etched significantly.
As described above, in a group III nitride semiconductor, a surface having a group III polarity shows more superb characteristics than a surface having a nitrogen polarity in terms of surface flatness, binding with impurities, re-growth characteristics, electrical characteristics and etching characteristics. Therefore, there is a call for developing a group III nitride semiconductor whose opposing two surfaces have group III polarities.